#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <iostream>
#include <queue>
#include <vector>

using namespace std;

struct ListNode {
    int val;
    ListNode* next;
    ListNode(int x) : val(x), next(NULL) {}
};

class Node {
   public:
    int val;
    Node* next;
    Node* random;

    Node(int _val) {
        val = _val;
        next = NULL;
        random = NULL;
    }
};

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

class Solution {
    queue<TreeNode*> q;

   public:
    vector<int> levelOrder(TreeNode* root) {
        vector<int> ret;
        if (root == NULL)
            return ret;
        q.push(root);
        while (!q.empty()) {
            TreeNode* tmp = q.front();
            ret.push_back(tmp->val);
            q.pop();
            if (tmp->left) {
                q.push(tmp->left);
            }
            if (tmp->right) {
                q.push(tmp->right);
            }
        }
        return ret;
    }
};

int main() {
    cout << "Hello, World!";
    // Solution()
    return 0;
}
